Generally, either substantive dyes or oxidation dyes are used for coloring keratinic fibers. Although intense colors with good fastness properties can be obtained with oxidation dyes, the development of the color generally takes place under the influence of oxidizing agents such as H2O2 for example, which in some cases can damage the fiber. Furthermore, some oxidation dye precursors or certain mixtures of oxidation dye precursors can have a sensitizing effect on people with sensitive skin. Substantive dyes are typically applied under gentler conditions. The disadvantage of these dyes, however, is that the colors often have inadequate fastness properties, in particular regard to hair washing, but also in respect to external influences like sunlight, or reactive environmental chemicals like swimming pool water. Such colors are also generally significantly more sensitive to shampooing than oxidative colors, so that an often undesired shift in shade or even a visible “decolorization” occurs much more quickly.
Achieving a uniform coloring of frequently pretreated hair, for example bleached or permanently waved hair, where the fibers present differing degrees of pre-damage, represents a particular challenge in terms of coloring hair with substantive dyes. During the coloring process itself, the coloring agent can exhibit an uneven coloring behavior on differently pre-damaged hair. Repeated hair washing can also cause the dyes to be washed out of the different areas of the hair to varying degrees, resulting in an inconsistent and undesirable color result.
In the development of coloring products based on substantive dyes, there is a particular focus on producing dye formulations having reduced selectivity, in order to achieve a uniform color result on sections of the hair that are damaged to varying degrees. In particular, this reduced selectivity should still be present not only immediately after the coloring process but also after repeated hair washes.